Riding a Slingshot into Space

September 18, 2009

Riding a Slingshot into Space

A project under development at NASA may someday give astronauts that option.

Engineers at NASA
have created a prototype of an electromagnetic propulsion system that would use a
linear motor and ramjet engine boost system–instead of an all rocket propulsion system–to fling
a vehicle into space. It is the first system that would operate beyond the
sound barrier using the combination of an air-breathing ramjet engine and an electromagnetic catapult. The work was
presented this week at the Space 2009 Conference in
Pasadena, CA.

The system is an alternative to traditionally-used chemical
propulsion, which requires large amounts of fuel that limits cargo capacity. It
is also a zero-emission, reusable system. The idea of electromagnetic launch
using linear motors has been around since 1946, but it was not until the late
1990s that NASA started seriously investigating the idea.

The electromagnetic
system works by tethering a spacecraft to a rail or track and using a linear
motor to accelerate it to supersonic speeds.

“Linear
motors are basically electric motors unwound,” says Kurt Kloesel, an
engineer in aeronautics and propulsion and lead researcher of the system at Dryden
Flight Research Center, in Edwards, CA. “There are two groups of coils and
an aluminum plate goes inside the gap [between the coils], when you hit the
juice you are energizing the coils and the inductive reaction of that throws
the aluminum plate out of this motor. ”

“You are
essentially propelling this vehicle along a track up to the point is disengages
from the track and takes off,” says Michael Wright, flight systems
integration and test manager of exploration systems and co-principal investigator
of the system at Goddard
Space Flight Center, in Greenbelt, MD.

Kloesel explains
that, as a vehicle starts to pick up speed, it incurs drag: “As you go faster
and faster, getting towards the speed of sound, the drag goes up significantly,
creating this shock wave structure on the vehicle. And once you pass the
supersonic barrier the drag goes down again.”

So what the
researchers are proposing, says Kloesel, is using the electromagnetic system to get past the
supersonic barrier. Then, the air-breathing ramjet engine–which feeds on
incoming air at very high speed–would take the vehicle out of Earth’s
atmosphere. The ramjet engine would not be on the rail, but part of the vehicle
itself.

The researchers have
tested the concept in lab experiments with “bench top models”, which
have reached approximately 156 miles per hour. Wright says the technology might
even be used someday on highway vehicles and airplanes.